Hudson Heather M, Park Michael C, Belhaj-Saïf Abderraouf, Cheney Paul D
Department of Physical Medicine and Rehabilitation, University of Kansas Medical Center, Kansas City, Kansas.
Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas; and.
J Neurophysiol. 2017 Jul 1;118(1):47-63. doi: 10.1152/jn.01070.2015. Epub 2017 Mar 29.
Stimulus-triggered averaging (StTA) of forelimb muscle electromyographic (EMG) activity was used to investigate individual forelimb muscle representation within the primary motor cortex (M1) of rhesus macaques with the objective of determining the extent of intra-areal somatotopic organization. Two monkeys were trained to perform a reach-to-grasp task requiring multijoint coordination of the forelimb. EMG activity was simultaneously recorded from 24 forelimb muscles including 5 shoulder, 7 elbow, 5 wrist, 5 digit, and 2 intrinsic hand muscles. Microstimulation (15 µA at 15 Hz) was delivered throughout the movement task and individual stimuli were used as triggers for generating StTAs of EMG activity. StTAs were used to map the cortical representations of individual forelimb muscles. As reported previously (Park et al. 2001), cortical maps revealed a central core of distal muscle (wrist, digit, and intrinsic hand) representation surrounded by a horseshoe-shaped proximal (shoulder and elbow) muscle representation. In the present study, we found that shoulder and elbow flexor muscles were predominantly represented in the lateral branch of the horseshoe whereas extensors were predominantly represented in the medial branch. Distal muscles were represented within the core distal forelimb representation and showed extensive overlap. For the first time, we also show maps of inhibitory output from motor cortex, which follow many of the same organizational features as the maps of excitatory output. While the orderly representation of major body parts along the precentral gyrus has been known for decades, questions have been raised about the possible existence of additional more detailed aspects of somatotopy. In this study, we have investigated this question with respect to muscles of the arm and show consistent features of within-arm (intra-areal) somatotopic organization. For the first time we also show maps of how inhibitory output from motor cortex is organized.
采用前肢肌肉肌电图（EMG）活动的刺激触发平均法（StTA），研究恒河猴初级运动皮层（M1）内的个体前肢肌肉代表区，目的是确定区域内躯体定位组织的范围。训练两只猴子执行一项需要前肢多关节协调的抓握任务。同时记录24块前肢肌肉的EMG活动，包括5块肩部肌肉、7块肘部肌肉、5块腕部肌肉、5块手指肌肉和2块手部固有肌。在整个运动任务过程中施加微刺激（15Hz，15μA），并将单个刺激用作触发EMG活动StTA的信号。利用StTA绘制个体前肢肌肉的皮层代表区图。如先前报道（Park等人，2001年），皮层图显示远端肌肉（腕部、手指和手部固有肌）代表区的中央核心被马蹄形的近端（肩部和肘部）肌肉代表区包围。在本研究中，我们发现肩部和肘部屈肌主要代表区位于马蹄形的外侧分支，而伸肌主要代表区位于内侧分支。远端肌肉位于核心远端前肢代表区内，且有广泛重叠。我们首次展示了运动皮层抑制性输出图，其具有许多与兴奋性输出图相同的组织特征。虽然沿中央前回主要身体部位的有序代表区已为人所知数十年，但关于躯体定位可能存在的其他更详细方面的问题也随之出现。在本研究中，我们针对手臂肌肉研究了这个问题，并展示了手臂内（区域内）躯体定位组织的一致特征。我们还首次展示了运动皮层抑制性输出的组织方式图。
